Optical, morphological and dielectric characterization of MBBA liquid crystal-doped hydrogels

In this work, MBBA liquid crystal-doped hydrogels are investigated through of Scanning Electron Microscopy (SEM), Polarized Optical Microscopy (POM), Optical Transmittance (OT) and Dielectric Spectroscopy (DS) techniques. For the synthesis of the hydrogels and of their composites a solution (20% water and 80% acetone) of the potassium periodate (KIO4) was prepared. The samples were prepared by radicalar photochemical polymerization of acrylamide monomer (AAm) in the presence of N, N′-methylene-bis-acrylamide (MBAAm) as a cross-linking agent. Potassium periodate (KIO4) was used as a photopolymerization initiator. In such synthesis, acrylamide monomer (AAm-Aldrich, 14, 866-5) was added with cross-linking agent MBAAm (N, N-methylene-bis-acrylamide) and liquid crystals MBBA (N-(4-methoxybenzilidene)-4(butylaniline)). The acetone was used to solubilize the liquid crystal MBBA in the solution. The resulting solution was placed and sealed between two glass plates coated with transparent and conducting films of tin oxide (SnO2) with spacer of 25 μm. All samples were investigated at 15.0 °C, 23.0 °C and 35.0 °C. The electrical behavior of the samples was characterized by using a Solartron 1260A impedance-gain phase analyzer in the frequency range from 10 mHz to 10 MHz with amplitude of 10 mV. The experimental results from DS technique are discussed by using Davidson-Cole and Havriliak-Negami approaches. As one of main results of this work we noticed that the cavities of the hydrogels synthesized with the use of acetone can be able to confine the free ions of the liquid crystal added to the polymeric matrix.